CN115449052B - A kind of mechanochromic polymer material based on folding-unfolding effect and its preparation method - Google Patents

Abstract

The invention relates to a mechanochromic polymer material based on the folding-unfolding effect and a preparation method thereof. The mechanochromic polymer material is polymerized by diol, diisocyanate and cyano-substituted phenylene vinylene dimer DCOP get. When the polymer film is uniaxially stretched (λ=365nm) under UV irradiation, the excimer is unfolded, and the fluorescence changes from yellow to green. With the relaxation of the stress, the film returns from green to yellow, and This process can be repeated many times. The strategy proposed in the present invention is easy to implement, enriches the molecular tweezers type mechanochromic materials, and further promotes the development of mechanochromic materials.

Description

A Mechanochromic Polymer Material Based on Folding-Unfolding Effect and Its Preparation method

technical field

The invention relates to the field of mechanochromic smart materials, in particular to a mechanochromic polymer material based on the folding-unfolding effect and a preparation method thereof.

Background technique

Excessive stress on a polymer can cause the molecular chains to break, resulting in the macroscopic fracture behavior of the material, so it is important to understand how and where this damage occurs. In recent years, the development of mechanochromic polymers with optical force response has attracted increasing attention for a wide range of applications, including pressure sensing materials and damage detection in structural materials, etc. The most commonly used force-responsive fluorophores usually have characteristic weak bonds, which are often covalently linked into polymer chains, making polymeric materials force-responsive. When the stress of the molecular chain exceeds a certain threshold, these weak bonds will undergo homolytic or heterolytic reactions. Such structural changes though can lead to changes in molecular absorption or fluorescence properties, which are used to detect stress distributions in materials. However, the breaking of weak bonds in such force-sensitive groups is a typical irreversible process, which directly destroys the utility of the material itself.

It is desirable for force-sensitive fluorophores to alert in a non-sacrificial or even reversible manner. In recent years, rotaxanes have been developed as an efficient mechanochromic fluorescent force sensor, which is a macrocycle carrying a fluorophore and contains a matching A mechanically interlocked fluorophore composed of dumbbell-shaped molecules of the quencher, which is integrated into the polymer backbone, causes the spatial separation of the fluorophore and the quencher due to molecular chain stretching, thereby enabling the fluorescence to be turned on. By choosing different fluorophores, the optical properties of rotaxanes can be directly tuned. At the same time, this fluorophore can be used to observe the ultra-small mechanical forces produced by cell division. But the long synthetic route and low synthetic yield have established huge obstacles to its application. In addition, Weder et al. reported a cyclic mechanochromic fluorophore containing two fluorophores, which can form intramolecular excimer associations. The emission changes from excimate to monodisperse dominance due to the relative dislocation of the dye molecules within the molecule.

Contents of the invention

Based on this, the present invention has developed a new generation of tweezer-type force-sensitive fluorophores that have similar advantages to the above and are easy to prepare, and thus synthesized a mechanochromic polymer material with a folding-unfolding effect. The designed tweezer-type force-sensitive fluorescent molecule is formed by chemically bonding two fluorescent groups with a short linker unit. Initially, the two fluorophores in the force-sensitive fluorophore stack together through non-covalent interactions to form a dimer excimer, and when an external force is transmitted to the tweezers, the dimer is pulled apart to form a monodisperse dominant fluorescence. Therefore, reversible force-sensitive photoresponsive properties can be obtained through the folding-unfolding of π-conjugated dye molecules.

To achieve the above object, the technical solution provided by the invention is:

A mechanochromic polymer material based on folding-unfolding effect, the mechanochromic polymer material is obtained by polymerization of diol, diisocyanate and cyano-substituted phenylene vinylene dimer DCOP, cyano-substituted phenylene The structure of ethylene dimer DCOP is as follows:

The dihydric alcohol is at least one of polyethylene glycol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

The diisocyanate is at least one of hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate (MDI), isophorone diisocyanate and toluene diisocyanate.

The preparation method of the mechanochromic polymer material based on the folding-unfolding effect comprises the following steps: dissolving a certain amount of cyano-substituted phenylene vinylene dimer DCOP, dibasic alcohol and diisocyanate in tetrahydrofuran, and dropping into the mixture Add dibutyltin dilaurate, and stir at room temperature for 3 hours; then add a THF solution dissolved in butanediol, and stir the mixture at room temperature for 24 hours; then add ethanol to the reaction mixture, and stir for 30 minutes, The reaction mixture was poured into ethanol; the yellow precipitate was collected by filtration; the solid was precipitated twice from THF to obtain a yellow solid DPU-m, which was the mechanochromic polymer material.

Further, the molar ratio of diisocyanate to diol is 1:0.9˜1:1.1.

Further, the mass fraction of DCOP in the polymer DPU is 0.1%-0.5%.

Further, the preparation of DCOP comprises the following steps:

1) Add 2,5-dihydroxy-1,4-terephthalaldehyde, 1-bromohexane, anhydrous potassium carbonate and DMF into the reaction vessel to obtain a mixture; heat the mixture at 80°C for 24h, after the reaction is completed , poured into water, extracted several times with CH ₂ Cl ₂ , dried over anhydrous Na ₂ SO ₄ , and evaporated the organic layer in vacuo to obtain a crude product; compound A was obtained by recrystallization in methanol;

2) Dissolve triethylene glycol in dry CH ₂ Cl ₂ , cool the solution to 0° C. with an ice bath under a nitrogen atmosphere, and add triethylamine; subsequently, add p-toluenesulfonyl chloride to the cooled reaction mixture; completely After the addition, the solution was heated to room temperature and stirred for 24 hours; the mixture was washed with water, and the organic layer was dried with Na ₂ SO ₄ , filtered, and concentrated in vacuo to obtain a crude product; purified by column chromatography to obtain compound B;

3) Add p-hydroxybenzonitrile, compound B and K ₂ CO ₃ into acetonitrile; reflux the mixture for 12 h, cool to room temperature, filter, wash with acetonitrile several times, dry the organic layer with anhydrous Na ₂ SO ₄ , vacuum Concentrate; Purify by column chromatography to obtain compound C;

4) Add p-hydroxybenzonitrile and anhydrous p-toluenesulfonic acid in CH ₂ Cl ₂ ; cool the solution to 0°C, then add 3,4-2H-dihydropyran dropwise; after complete addition, heat the mixture to Stir at room temperature for 6 hours; wash the solution with Na ₂ CO ₃ aqueous solution; dry the organic phase with anhydrous sodium sulfate, then distill under reduced pressure; purify by column chromatography to obtain compound D;

5) Dissolve compound A, compound C and compound D in a mixture of t-BuOH and THF at 70°C; quickly add t-BuOK and n-Bu ₄ NOH, the solution turns purple immediately; stir the mixture at 70°C 15 minutes, cooled to room temperature, poured into water; extracted twice with CH ₂ Cl ₂ solution; dried the organic layer over anhydrous Na ₂ SO ₄ , and distilled under reduced pressure; purified by column chromatography to obtain compound E and MCOP;

6) Compound E and p-toluenesulfonic acid were added in methanol; the mixture was stirred overnight at room temperature; a red solid precipitate was formed during this period; this solid was filtered and washed with methanol; the solid was dried in vacuo to give compound F as a red solid ;

7) Dissolve tetraethylene glycol and triethylamine in CH ₂ Cl ₂ , and cool the solution to 0°C, and add p-toluenesulfonyl chloride solution dropwise; stir the resulting mixture at room temperature for 16 hours; HCl(aq), saturated NaHCO ₃ , H ₂ O washed; the organic layer was dried over anhydrous Na ₂ SO ₄ , and then distilled under reduced pressure; column chromatography was purified to obtain compound G;

8) Compound F, compound G, K ₂ CO ₃ and acetonitrile were added into the flask; the mixture was refluxed for 24 h, cooled to room temperature, filtered, washed several times with acetonitrile, and vacuum dried to obtain DCOP as a red solid.

Further, the reaction molar ratio of 2,5-dihydroxy-1,4-terephthalaldehyde, 1-bromohexane, and anhydrous potassium carbonate in step 1) is: 1/2.5/2.5; The reaction molar ratio of hydroxyphenylacetonitrile, compound B and K ₂ CO ₃ is: 1/1.2/1.5.

Further, the reaction molar ratio of compound A, compound C and compound D in step 5) is: 1/1.1/1.2; the reaction molar ratio of compound E and p-toluenesulfonic acid in step 6) is: 100/0.5.

Further, the reaction molar ratio of compound F, compound G and K ₂ CO ₃ in step 8) is: 2/1/2.5.

The present invention also protects the application of the mechanochromic polymer material based on the folding-unfolding effect in reversible mechanochromic materials.

Compared with prior art, the beneficial effect of the present invention is:

The DCOP tweezers-based mechanochromic polymer material designed in the present invention exhibits good reversible mechanochromic performance. The force response characteristics of the DCOP tweezers in the polymer material mainly come from the intramolecular folding-unfolding effect of the COP group under external force stimulation. In the ground state, there is a certain degree of intramolecular interaction between the COP groups to form excimer associations. When the polymer film is uniaxially stretched (λ=365nm) under UV irradiation, the excimer is unfolded, and the fluorescence changes from yellow to green. With the relaxation of the stress, the film returns from green to yellow, and This process can be repeated many times. The strategy proposed in the present invention is easy to implement, enriches the molecular tweezers type mechanochromic materials, and further promotes the development of mechanochromic materials.

Description of drawings

Fig. 1. UV-Vis absorption spectrum and fluorescence emission spectrum (c=5um/L, λex=365nm) of DCOP and MCOP in THF solution.

Figure 2. (a) Images of DPU-0.2 and MPU-0.2 under UV and visible light; fluorescence decay spectra of DPU-0.2(b) and MPU-0.2(c) films.

Figure 3. Normalized fluorescence spectra of DPU-0.2 films (increasing strain).

Detailed ways

The above-mentioned content of the present invention will be described in further detail below by the form of the embodiment, but this should not be interpreted as the scope of the above-mentioned theme of the present invention being limited to the following embodiments, all technologies realized based on the above-mentioned content of the present invention belong to scope of the invention.

The mechanochromic polymer material prepared by the present invention is tested according to the following method:

The H NMR and C NMR spectra were measured with a Bruker AVANCE II NMR instrument, tetramethyl silicon was used as an internal standard, and the solvent was deuterated chloroform or deuterated dimethyl sulfoxide. Fluorescence spectra were measured with a Shimadzu RF-5301PC fluorescence spectrophotometer.

The preparation of DCOP comprises the following steps:

1) Add 2,5-dihydroxy-1,4-terephthalaldehyde, 1-bromohexane, anhydrous potassium carbonate and DMF into the reaction vessel to obtain a mixture; heat the mixture at 80°C for 24h, after the reaction is completed , poured into water, extracted several times with CH ₂ Cl ₂ , dried over anhydrous Na ₂ SO ₄ , and evaporated the organic layer in vacuo to obtain a crude product; compound A was obtained by recrystallization in methanol;

2) Dissolve triethylene glycol in dry CH ₂ Cl ₂ , cool the solution to 0° C. with an ice bath under a nitrogen atmosphere, and add triethylamine; subsequently, add p-toluenesulfonyl chloride to the cooled reaction mixture; completely After the addition, the solution was heated to room temperature and stirred for 24 hours; the mixture was washed with water, and the organic layer was dried with Na ₂ SO ₄ , filtered, and concentrated in vacuo to obtain a crude product; purified by column chromatography to obtain compound B;

3) Add p-hydroxybenzonitrile, compound B and K ₂ CO ₃ into acetonitrile; reflux the mixture for 12 h, cool to room temperature, filter, wash with acetonitrile several times, dry the organic layer with anhydrous Na ₂ SO ₄ , vacuum Concentrate; Purify by column chromatography to obtain compound C;

4) Add p-hydroxybenzonitrile and anhydrous p-toluenesulfonic acid in CH ₂ Cl ₂ ; cool the solution to 0°C, then add 3,4-2H-dihydropyran dropwise; after complete addition, heat the mixture to Stir at room temperature for 6 hours; wash the solution with Na ₂ CO ₃ aqueous solution; dry the organic phase with anhydrous sodium sulfate, then distill under reduced pressure; purify by column chromatography to obtain compound D;

5) Dissolve compound A, compound C and compound D in a mixture of t-BuOH and THF at 70°C; quickly add t-BuOK and n-Bu ₄ NOH, the solution turns purple immediately; stir the mixture at 70°C 15 minutes, cooled to room temperature, poured into water; extracted twice with CH ₂ Cl ₂ solution; dried the organic layer over anhydrous Na ₂ SO ₄ , and distilled under reduced pressure; purified by column chromatography to obtain compound E and MCOP;

6) Compound E and p-toluenesulfonic acid were added in methanol; the mixture was stirred overnight at room temperature; a red solid precipitate was formed during this period; this solid was filtered and washed with methanol; the solid was dried in vacuo to give compound F as a red solid ;

7) Dissolve tetraethylene glycol and triethylamine in CH ₂ Cl ₂ , and cool the solution to 0°C, and add p-toluenesulfonyl chloride solution dropwise; stir the resulting mixture at room temperature for 16 hours; HCl(aq), saturated NaHCO ₃ , H ₂ O washed; the organic layer was dried over anhydrous Na ₂ SO ₄ , and then distilled under reduced pressure; column chromatography was purified to obtain compound G;

8) Compound F, compound G, K ₂ CO ₃ and acetonitrile were added into the flask; the mixture was refluxed for 24 h, cooled to room temperature, filtered, washed several times with acetonitrile, and vacuum dried to obtain DCOP as a red solid.

In step 1), the reaction molar ratio of 2,5-dihydroxy-1,4-terephthalaldehyde, 1-bromohexane, and anhydrous potassium carbonate is: 1/2.5/2.5; in step 3), p-hydroxyphenylacetonitrile , The reaction molar ratio of compound B and K ₂ CO ₃ is: 1/1.2/1.5.

The reaction molar ratio of compound A, compound C and compound D in step 5) is: 1/1.1/1.2; the reaction molar ratio of compound E and p-toluenesulfonic acid in step 6) is: 100/0.5.

The reaction molar ratio of compound F, compound G and K ₂ CO ₃ in step 8) is: 2/1/2.5.

Example 1: Preparation of Mechanochromic Polymer Material DPU-0.1

The preparation route is as follows:

Dissolve 5mg of DCOP, hydroxyl-terminated polytetrahydrofuran (Mn=2000g/mol, 3.20g, 1.60mmol) and MDI (1.23g, 4.90mmol) in 30mL of tetrahydrofuran, and add dibutyltin dilaurate (2 drops) dropwise to the mixture , and stirred at room temperature for 3 hours. Then 10 mL of THF solution dissolved in butanediol (288 mg, 3.20 mmol) was added, and the mixture was stirred and reacted at room temperature for 24 hours. Then 5 mL of ethanol was added to the reaction mixture, and after stirring for 30 minutes, the reaction mixture was poured into ethanol (200 mL). The yellow precipitate was collected by filtration. The solid was precipitated from THF two more times to obtain DPU-0.1 as a yellow solid.

Example 2: Preparation of Mechanochromic Polymer Material DPU-0.2

The specific preparation steps are as follows: the same parts as in Example 1 will not be repeated, and the difference from Example 1 is that the amount of DCOP added is 10 mg.

Example 3: Preparation of Mechanochromic Polymer DPU-0.4

The specific preparation steps are as follows: the same part as in Example 1 will not be repeated, and the difference from Example 1 is that the amount of DCOP added is 20 mg.

Comparative example 1: Preparation of the reference polymer material MPU-0.2

The preparation route is as follows:

Dissolve 10mg of MCOP, hydroxyl-terminated polytetrahydrofuran (Mn=2000g/mol, 3.20g, 1.60mmol) and MDI (1.23g, 4.90mmol) in 30mL of tetrahydrofuran, and add dibutyltin dilaurate (2 drops) dropwise to the mixture , and stirred at room temperature for 3 hours. Then 10 mL of THF solution dissolved in butanediol (288 mg, 3.20 mmol) was added, and the mixture was stirred and reacted at room temperature for 24 hours. Then 5 mL of ethanol was added to the reaction mixture, and after stirring for 30 minutes, the reaction mixture was poured into ethanol (200 mL). The yellow precipitate was collected by filtration. The solid was precipitated from THF two more times to afford MPU-0.2 as a yellow solid.

Comparative example 2: Preparation of the reference polymer material MPU-0.4

The specific preparation steps are as follows: the same part as Comparative Example 1 will not be repeated, and the difference from Comparative Example 1 is that the amount of MCOP added is 20 mg.

Hereinafter, the mechanochromic polymer material based on the folding-unfolding effect and the preparation method thereof of the present invention will be further described with reference to some examples.

First, the optical properties of MCOP and DCOP (c = 5um/L) in THF solution were studied by UV-Vis absorption and fluorescence spectroscopy (Fig. 1). In the absorption spectrum, MCOP exhibits the S ₀ -S ₁ transition vibration band, and there are two absorption peaks at ~365 and 431 nm, which belong to the A ^0-1 and A ^0-0 vibration bands (Fig. 1(a) ); there is an obvious emission band at ~505nm in the emission spectrum, and it emits obvious bright green fluorescence ((b) in Figure 1). The maximum vibration band of DCOP (~366,431nm) is similar to the wavelength of MCOP, but the vibration band of A ^0-1 is stronger than that of MCOP. This suggests that the COP moiety in DCOP has a certain degree of interaction in the ground state, which is beneficial to the formation of excimates. In addition, the stronger emission band of DCOP at ∼550 nm further validates the formation of excimates ((b) in Figure 1). The intensity ratio of A ^0-1 and A ^0-0 vibrational bands (A ^0-1 /A ^0-0 ) can be used to estimate the strength of the intermolecular or intramolecular interaction of the COP group in MCOP or DCOP, A ^0-1 / The higher the A ^0-0 value, the stronger the non-covalent interaction between COP groups or within the molecule. Calculated from the absorption spectrum, the A ^0-1 /A ^0-0 values of MCOP and DCOP were 0.66 and 0.75, respectively.

DPU-m and MPU-n, that is, polyurethane mechanochromic high Molecular materials, where m and n represent the mass percentages of DCOP and MCOP in polyurethane, respectively. All polyurethanes synthesized had number-average molecular weights between 31,000 and 58,100 g/mol and a degree of polymerization between 1.6 and 2, which is consistent with the expected results for polymers obtained by polymerization (Table 1). DPU-0.4, DPU-0.2, DPU-0.1, MPU-0.4 and MPU-0.2 films were obtained by directly coating the THF solution of the corresponding concentration polymer on the polytetrafluoroethylene film, and the solvent was evaporated. The results show that the optical properties of DPU and MPU films have nothing to do with the dye content (lower concentration), so we take DPU-0.2 and MPU-0.2 as examples to further confirm the decisive role of DCOP tweezers on the mechanochromic properties of materials. ((a) in Figure 2) shows that the DPU-0.2 and MPU-0.2 films exhibit yellow and yellow-green fluorescence under visible light, respectively, and green and yellow fluorescence under 365nm UV. The fluorescence lifetime measurement results of the film show ((b) in Figure 2, (c) in Figure 2), the decay curve of the MPU-0.2 film presents a single exponential function, which verifies that only one species with a lifetime of 3.2ns exists, the Species may belong to a monodisperse state of COP groups. The difference is that the decay curve of the DPU-0.2 film presents a double-exponential function, indicating the existence of two different species with lifetimes of 2.8ns and 14.2ns, which are considered to be related to monodisperse COP (2.8ns) and weakly coupled Associated bikinyl associations (14.2 ns). This conclusion indicates that dimer excimer associations are formed between the COP groups in the DPU-0.2 film.

After understanding the photophysical properties of MCOP, DCOP and their polymer films, we further studied the mechanochromic properties of MPU-0.2 and DPU-0.2 films. The pristine DPU-0.2 films exhibited the typical stress-strain behavior of rubbery polymers. When uniaxially stretched under UV irradiation (λ=365nm), due to the unfolding of the COP tweezers, a fluorescence change from yellow to green is detected. When the external force is relaxed, the green fluorescence can return to the original state. This process can be repeated many times. Second-rate. However, the MPU-0.2 film did not show a similar phenomenon during stretching, and the fluorescence of the film remained green when the strain reached 300%. The fluorescence signal is transmitted to the detector by optical fiber, and the fluorescence response of the film during in-situ uniaxial stretching is analyzed. With the continuous increase of the strain, the fluorescence spectrum of DPU-0.2 showed an obvious blue shift, the intensity of the emission band at 550nm gradually weakened, and the intensity of the emission band at 510nm gradually increased (Figure 3). It was found that during this process, the I ₅₅₀ /I ₅₁₀ value was approximately linear with the strain, indicating that the stress was effectively transferred to the COP dimer mechanogroup. After stress relaxation, the fluorescence spectrum returns to the initial state, which indicates that the folding and unfolding of COD is mechanistically reversible. These results suggest that the linker unit in the DCOP fluorophore facilitates the formation of excimers and ultimately enables the folding-unfolding behavior.

The following table shows the number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index (PDI) of the polymers DPU-m and MPU-n.

Table 1

It can be seen that the polyurethane polymer material based on the folding-unfolding effect provided by the present invention has good reversible mechanochromic properties. This technical route is easy to realize, enriches the molecular tweezers type mechanochromic materials, and further promotes the development of mechanochromic materials.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Any skilled person who is familiar with the profession, without departing from the scope of the technical solutions of the present invention, according to the technical essence of the present invention, Any simple modifications, equivalent replacements and improvements made in the above embodiments still fall within the protection scope of the technical solution of the present invention.

Claims (10)

1. The stress-induced color-changing high polymer material based on folding-unfolding effect is characterized in that the stress-induced color-changing high polymer material is obtained by polymerizing dihydric alcohol, diisocyanate and cyano-substituted phenylene ethylene dimer DCOP, and the structure of the cyano-substituted phenylene ethylene dimer DCOP is as follows:

2. the stress-induced color change polymer material based on folding-unfolding effect according to claim 1, wherein the dihydric alcohol is at least one of polyethylene glycol, ethylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol, and 1, 6-hexanediol.

3. The stress-induced color change polymer material based on folding-unfolding effect according to claim 1, wherein the diisocyanate is at least one of hexamethylene diisocyanate HDI, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate MDI, isophorone diisocyanate, toluene diisocyanate.

4. A method for preparing a mechanochromatic polymeric material based on the folding-unfolding effect as claimed in any one of claims 1 to 3, characterized by comprising the following steps: a certain amount of cyano-substituted phenylene ethylene dimer DCOP, dihydric alcohol and diisocyanate are dissolved in tetrahydrofuran, dibutyl tin dilaurate is added dropwise into the mixture, and the mixture is stirred for 3 hours at room temperature; then adding a THF solution dissolved with butanediol, and stirring the mixture at room temperature for reaction for 24 hours; subsequently, ethanol is added into the reaction mixture, and after stirring is carried out for 30 minutes, the reaction mixture is poured into the ethanol; collecting yellow precipitate by filtration; and separating out the solid from THF twice to obtain yellow solid DPU, namely the mechanochromic polymer material.

5. The method for preparing a mechanochromatic polymer material based on a folding-unfolding effect according to claim 4, wherein the molar ratio of diisocyanate to dihydric alcohol is 1:0.9-1:1.1.

6. The method for preparing a stress-induced color change polymer material based on a folding-unfolding effect according to claim 4, wherein the mass fraction of DCOP in the polymer DPU is 0.1% -0.5%.

7. The method for preparing the stress-induced color change polymer material based on the folding-unfolding effect according to claim 4, wherein the preparation of the DCOP comprises the following steps:

1) Adding 2, 5-dihydroxy-1, 4-terephthalaldehyde, 1-bromohexane, anhydrous potassium carbonate and DMF into a reaction vessel to obtain a mixture; the mixture was heated at 80℃for 24h, after the reaction was completed, poured into water and treated with CH ₂ Cl ₂ Extracting for several times, anhydrous Na ₂ SO ₄ After drying, the organic layer was evaporated in vacuo to give the crude product; obtaining a compound A by recrystallization in methanol;

2) Dissolving triethylene glycol in dried CH ₂ Cl ₂ Cooling the solution to 0 ℃ with an ice bath under nitrogen atmosphere, and adding triethylamine; subsequently, p-toluenesulfonyl chloride was added to the cooled reaction mixture; after complete addition, the solution was warmed to room temperature and stirred for 24 hours; the mixture was washed with water and Na ₂ SO ₄ Drying the organic layer, filtering, and vacuum concentrating to obtain a crude product;

purifying by column chromatography to obtain a compound B;

3) Parahydroxyphenylacetonitrile, compounds B and K ₂ CO ₃ Adding the mixture into acetonitrile; the mixture was refluxed for 12h, cooled to room temperature, filtered, washed several times with acetonitrile, and the organic phase was taken upAnhydrous Na for layer ₂ SO ₄ Drying and vacuum concentrating; purifying by column chromatography to obtain a compound C;

4) On CH ₂ Cl ₂ Adding p-hydroxyphenylacetonitrile and anhydrous p-toluenesulfonic acid; cooling the solution to 0 ℃, and then dropwise adding 3, 4-2H-dihydropyran; after complete addition, the mixture was warmed to room temperature and stirred for 6 hours; with Na ₂ CO ₃ Washing the solution with an aqueous solution;

the organic phase was dried over anhydrous sodium sulfate, and then distilled under reduced pressure; purifying by column chromatography to obtain a compound D;

5) Dissolving compound a, compound C and compound D in a mixture of t-BuOH and THF at 70 ℃; fast addition of t-BuOK and n-Bu ₄ NOH, the solution immediately turned purple; stirring the mixture at 70deg.C for 15 min, cooling to room temperature, and pouring into water; by CH ₂ Cl ₂ Extracting the solution twice; the organic layer was treated with anhydrous Na ₂ SO ₄ Drying and then distilling under reduced pressure;

purifying by column chromatography to obtain compound E and MCOP;

6) Adding a compound E and p-toluenesulfonic acid into methanol; the mixture was stirred at room temperature overnight; during this time a red solid precipitate formed; this solid was filtered and washed with methanol; vacuum drying the solid to obtain a red solid compound F;

7) Dissolving tetraethylene glycol and triethylamine in CH ₂ Cl ₂ Cooling the solution to 0 ℃, and dropwise adding a p-toluenesulfonyl chloride solution; the resulting mixture was stirred at room temperature for 16 hours; the solution was sequentially treated with 5% aqueous HCl, saturated NaHCO ₃ 、H ₂ O washing; the organic layer was treated with anhydrous Na ₂ SO ₄ Drying, and then distilling under reduced pressure; purifying by column chromatography to obtain a compound G;

8) Compound F, compound G, K ₂ CO ₃ And acetonitrile was added to the flask; the mixture was refluxed for 24h, cooled to room temperature, filtered, washed several times with acetonitrile and dried in vacuo to give DCOP as a red solid.

8. The high stress-induced color change based on fold-unfold effect according to claim 7The preparation method of the molecular material is characterized in that the reaction mole ratio of the 2, 5-dihydroxyl-1, 4-terephthalaldehyde, 1-bromohexane and anhydrous potassium carbonate in the step 1) is as follows: 1/2.5/2.5; p-hydroxyphenylacetonitrile, compounds B and K in step 3) ₂ CO ₃ The molar ratio of the reaction is as follows: 1/1.2/1.5.

9. The method for preparing a mechanochromatic polymer material based on the folding-unfolding effect according to claim 7, wherein the molar ratio of the reaction of the compound A, the compound C and the compound D in the step 5) is as follows: 1/1.1/1.2; the molar ratio of compound E to p-toluenesulfonic acid in step 6) is: 100/0.5; compound F, compound G, K in step 8) ₂ CO ₃ The molar ratio of the reaction is as follows: 2/1/2.5.

10. Use of a mechanochromatic polymeric material according to any one of claims 1 to 3, based on the fold-unfold effect, in reversible mechanochromatic materials.

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